The European Union’s biggest foreign mission has been accused of using its powers to try to silence a whistleblower who claims to have uncovered evidence of possible corruption.

Eulex, the foreign mission in Kosovo, is being taken to an employment tribunal by the London-based lawyer Maria Bamieh. She claims she was forced from her job as a prosecutor after exposing evidence of bribery among senior staff.

But now Bamieh and her solicitor have been formally warned by Eulex that they could be prosecuted and jailed if they disclose any details of her employment case to “non-parties,” including potential witnesses.

The prospect of criminal prosecution in Kosovo is particularly serious, given that it would be carried out by Eulex prosecutors and judges.

Eulex has the power to apply for the extradition of suspects from the UK or apply for a European arrest warrant.

Eulex has cost more than €1bn (£703m) since it was established with a promise of pursuing the “big fish” among Kosovo politicians who were alleged to be involved in organised crime.

Bamieh’s claims, along with the appearance of compromising documents in the Kosovan media, have reinforced the impression within the former Yugoslav province that Eulex may have become part of the problem it is trying to solve.

In a statement, Bamieh, a former Crown Prosecution Service lawyer, said Eulex’s threat of prosecution was the culmination of a three-year campaign to stop her from exposing what she claims is a culture of corruption and from disclosing her mistreatment.

“These latest developments only serve to demonstrate the lengths to which the relevant powers will go to prevent my concerns from being openly discussed,’’ she said. “Despite this, I shall not be cowed and I shall not be intimidated.”

Her solicitor, Peter Daly, from the firm Bindmans, said the action sought to stop him and Bamieh from getting in touch with witnesses.

“The threats against me and my client – together with the highly unusual request for blanket anonymity and desire to obscure these proceedings from any scrutiny – do not appear to sit comfortably with Eulex’s function as a protector of the rule of law,” he said.

Bamieh joined Eulex in 2008 but has claimed she was forced out last summer after attempting to uncover corruption and bribery among senior staff.

She claimed that she discovered evidence of corruption after a telephone tap of one suspected criminal, who had been a senior civil servant, aroused suspicions that senior figures in Eulex were taking bribes worth hundreds of thousands of euros.

But after complaining to the authorities and asking for a full inquiry, Bamieh said she was victimised, smeared in the press and forced out. Her dismissal followed two years of unfair treatment, including full-scale investigations into her conduct for petty misdemeanours such as parking infringements, she has previously alleged.

Eulex has said she was suspected of leaking classified documents. Bamieh denies the accusation, insisting she only went to the press after being suspended.

In a further development, Eulex has written to the tribunal seeking blanket privacy and anonymity orders over all remaining stages of the proceedings. This would prevent the media from reporting on any aspect of the case, despite the extensive global coverage that it has already received.

Shah Qureshi, head of employment law at Bindmans, said the legal threats were particularly unusual and sinister.

“It is a fundamental aspect of a functioning rule of law that solicitors are not threatened with criminal prosecution simply for representing their clients,’’ he said. “The threat made by Eulex’s lawyers contravenes this basic principle.’’

He added: “This is a substantial attack on the rule of law in the UK and we deplore it without reservation. The fact that this attack has been made by an organisation founded to protect the rule of law ought to be the source of deepest concern in Brussels and in Kosovo.”

Kosovo broke away from Yugoslavia in 1999 and became a UN protectorate after its bloody war, which pitched the Serb minority against the majority ethnic Albanians. In 2008 the ethnic Albanian-led parliament declared unilateral independence and the UN unit was replaced by Eulex that same year.

A spokesman for Eulex declined to comment on the threats of prosecution or the claims of intimidation by Bamieh or her solicitor.

“Eulex is currently in the process of defending litigation that has been brought against it by Maria Bamieh,’’ the spokesman said. “Consequently, arguments in those proceedings are ongoing and we will make no comment about them until the proceedings are concluded. Eulex being a rule of law mission gives due respect to the employment tribunal of central London and wishes not to comment [on] the case until the Judgment is rendered.”